<template>
  <ul class="list">
    <li class="item" v-for="item in letters"
        :key='item'
        :ref='item'
        @click="handleLetterClick"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
  export default{
    name:'CityAlphabet',
    props:{
      cities:Object
    },
    data(){
      return {
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    computed:{
      letters(){
        const letters=[];
        for(let i in this.cities){
          letters.push(i);
        }
        return letters;
      }
    },
    updated(){
      this.startY = this.$refs['A'][0].offsetTop;
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart(){
        this.touchStatus = true;
      },
      handleTouchMove(e){
        if(this.touchStatus){
          if(this.timer){
            clearTimeout(this.timer);
          }
          this.timer = setTimeout(() =>{
            const touchY = e.touches[0].clientY - 79;
            const index = Math.floor((touchY - this.startY) / 20);
            if(index >= 0 && index < this.letters.length){
              this.$emit('change',this.letters[index]);
            }
          },16)
        }
      },
      handleTouchEnd(){
        this.touchStatus = false;
      }
    }
  }
</script>

<style lang="stylus" scoped rel="stylesheet/stylus">
  @import '~styles/varibles.styl'
  .list
    display :flex;
    flex-direction :column;
    justify-content :center;
    position :absolute;
    top :1.58rem;
    right :0;
    bottom :0;
    width :0.4rem;
    .item
      text-align :center;
      line-height :0.4rem;
      color:$bgColor;
</style>
